1. Field of the Invention
The present invention relates to a vehicle drive assist system that controls acceleration and deceleration when following a preceding vehicle.
2. Description of the Related Art
In recent years, various proposals have been made for vehicle drive assist systems in which an outside environment in front of a subject vehicle is recognized by a front-environment recognition device such as a millimeter-wave radar, an infrared laser radar, a stereo camera, or a monocular camera, and in which running of the subject vehicle is controlled on the basis of the recognized outside environment.
One of these vehicle drive assist systems is an inter-vehicle distance control (ACC; Adaptive Cruse Control) system. The ACC system performs constant-speed running control or performs follow-up running control so that a subject vehicle follows a preceding vehicle, in accordance with the result of recognition of the preceding vehicle.
The ACC system determines, according to information from the front-environment recognition device, whether or not a preceding vehicle is present in a traveling region of a subject-vehicle traveling path. When a preceding vehicle is detected, the ACC system performs follow-up running control so that the subject vehicle follows the preceding vehicle. In contrast, when a preceding vehicle is not detected, the ACC system performs constant-speed running control so that the subject vehicle travels at a set vehicle speed set by the driver. For example, the ACC system is disclosed in Japanese Unexamined Patent Application Publication No. 2003-308598 (Patent Document 1).
The ACC system performs acceleration and deceleration control and brake control in accordance with the inter-vehicle distance between the preceding vehicle recognized by the front-environment recognition device and the subject vehicle so that the inter-vehicle distance converges to a target inter-vehicle distance. When the preceding vehicle moves out of the subject-vehicle traveling path, acceleration control is performed to return to the set vehicle speed.
Therefore, for example, when the preceding vehicle changes its lane in order to avoid an on-road obstacle, the subject vehicle that is following the preceding vehicle determines that the preceding vehicle moves out of the subject-vehicle traveling path, and acceleration control is started to shift to the set vehicle speed.
In this case, when the driver recognizes the on-road obstacle that has been avoided by the preceding vehicle, the driver turns the steering wheel so as to avoid the on-road obstacle. However, since the ACC system does not recognize the preceding vehicle in front of the subject vehicle, acceleration control is performed against the driver's intention. As a result, even in a situation in which the driver can normally avoid the obstacle simply by turning the steering wheel without pressing the brake pedal, since the subject vehicle is accelerated, the driver needs to press the brake pedal more than necessary. This gives the driver a feeling of discomfort.
Further, when the driver presses the brake pedal, the ACC is automatically cancelled against the driver's intention to continue the ACC.